Pesticide usage in Scotland: Rodenticide use by Local Authorities 2023

Rodenticide use 2023

Rodenticide active substances encountered

Nine active substances were used by the LAs providing data for this survey: alphachloralose, brodifacoum, bromadiolone, cholecalciferol, coumatetralyl, difenacoum, difethialone, flocoumafen and warfarin (Table 1 & Figure 2).

The majority of rodenticides encountered in this survey were anticoagulants (ARs), which prevent the synthesis of blood clotting factors and result in rodent death by haemorrhage. Five of the compounds reported were second generation anticoagulant rodenticides (SGARs), accounting for 80% (595 g) of the active substance applied. This was a 20% decrease compared to the 2015 ⁽¹⁾ figure (746g). Coumatetralyl and warfarin were the only two first generation anticoagulant rodenticides (FGARs) reported, accounting for 1% (<10 g) of active substance used, compared to 3% (24g) in 2015⁽²⁾. Two non-AR rodenticides, alphachloralose and cholecalciferol, accounted for 18% (139 g) of active substance used (9% each). No non-AR rodenticides were reported in 2015⁽¹⁾. The large increase in non-AR actives is associated with a much smaller proportional use in non-AR products. These non-AR active substances are formulated with much higher levels of active ingredients than the SGAR products. While SGARs are typically found at up to 0.005% active ingredient in professional formulations, the currently available cholecalciferol products have 0.075% active (15 times maximum SGAR concentration), and alphachloralose products are typically up to 4% active ingredient, which is 800 times the concentration of SGARs. Hence a relatively small use of alphachloralose product use may equate to a comparatively large amount of active ingredient.

Despite a reduction in contribution from 81% to 62% of total usage compared to the 2015 survey⁽¹⁾, bromadiolone remained the most common active substance used by LAs in Scotland in 2023. Use of difenacoum fell from 11% to 6% while brodifacoum increased from 5% to 11% (Figure 3).

Figure 2 Rodenticide active substances used by Local Authorities in 2023 (percentage by weight)

A bar chart showing the percentage by weight of each rodenticide active substance used in 2023. Bromadiolone is the most prevalent active substance, accounting for over 60% of the total.

Figure 3 Dominant SGAR active substances used by LAs in 2023 compared to 2015 (percentage by weight)

A column chart comparing percentage weight of the most frequently used active substances between 2015 and 2023

Quantity of rodenticide products used

Responding LAs used ca. 12.2 tonnes of rodenticide products in 2023 (Table 1), compared to 14.9 tonnes in 2015⁽¹⁾, an 18.1% decrease. As active concentrations of the vast majority of these rodenticidal products are very low (0.0025% to 0.005% of product weight for SGARs). This equates to less than 1 kg of rodenticidal active substance. The remainder of the product is food bait which attracts rodents to consume the rodenticide.

The majority of products encountered contained a single active substance, with the exception of very limited use (1 kg) of a product containing both bromadiolone and difenacoum (Table 1, Figure 4).

The most commonly used products were those containing bromadiolone, accounting for ca. 9.3 tonnes of the rodenticide products applied (76% of total use, compared to 84% in 2015). In addition, ca. 1.8 tonnes of products containing brodifacoum (15%) were used and ca. 0.86 tonnes of difenacoum products (7%). This again demonstrates a change in the relative usage of brodifacoum and difenacoum compared to 2015⁽¹⁾, when they accounted for 0.7 tonnes (5%) and 1.6 tonnes (11%) respectively (Figure 5). The remaining SGAR products (containing flocoumafen, difethialone and a bromadiolone/difenacoum mixed formulation, accounted for 155 kg (1%) of use. FGAR products (coumatetralyl and warfarin) comprised just 7 kg of use and the non-ARs (alphachloralose and cholecalciferol) equalled 96 kg, of which >94 kg was cholecalciferol. Collectively these other compounds comprised less than 1% of product use, thus more than 99% of the rodenticidal products used were SGARs (Table 1).

Figure 4 Rodenticide products used by LAs in 2023 (percentage by weight of bait)

A bar chart showing the percentage by weight of each rodenticide bait used in 2023 by LAs. Bromadiolone baits are the dominant bait type, accounting for 76% of the total.

Figure 5 Dominant SGAR products used by LAs in 2023 compared to 2015 (percentage by weight)

A column chart comparing percentage weight of the most frequently used bait products between 2015 and 2023.

Rodenticide use by setting

Survey respondents were asked to record, where possible, their rodenticide baiting activities in relation to the setting of use (Table 2, Figure 6). All 27 of the LAs who responded to the survey conducted domestic baiting activities and the majority of rodenticide use was in domestic settings (ca.8.8 tonnes, 72%). A further 5% of rodenticides (ca. 0.6 tonnes) were recorded as being used in a combination of domestic and industrial settings and 8% (ca. 1 tonne) in solely industrial settings. Over half of LAs (56%) reported that they baited in industrial settings in 2023, but two (7%) were unable to separate out their domestic and Industrial use. Of the remaining LAs it is considered possible that some non-domestic (i.e. industrial) baiting may be incorporated in the domestic figure. The data are reported here as provided by LAs.

No use of sewer baiting was encountered in this survey. This contrasts with the 2015 LA survey⁽¹⁾ where five of the LAs (20%) reported sewer baiting activities with a total combined use of 34 kg.

During this survey, we asked about all rodenticide use by LAs. Three of the responding LAs conducted baiting on agricultural holdings on behalf of farmers. This amounted to just under 1.9 tonnes of bait and 15% of the total recorded use, the same percentage as 2015⁽¹⁾. Whilst this is recorded here for completeness in relation to LA baiting activities, it should be noted that agricultural baiting conducted by LAs is also included in the agricultural rodenticide surveys therefore caution should be exercised if compiling data from both LA and agricultural rodenticide reports to avoid double counting of LA baiting on farms.

Overall, the total LA baiting in non-agricultural settings was reported to be ca. 10.3 tonnes (Table 2). These data represent around 84% and 91% of Scottish LAs and human population respectively. This is a decrease from the estimated 12.7 tonnes in the 2015 survey⁽¹⁾, although a slightly different group of LAs responded to each survey. These data indicate that the overall quantity of rodenticide used by LAs is considerably lower than that reported in the most recent Scottish agricultural surveys of rodenticide use in arable⁽²⁾ and grassland⁽³⁾ sectors (an estimated 40 and 85 tonnes respectively).

Figure 6 Setting of rodenticide product use by LAs in 2023

A column chart showing the percentage of products applied in each setting by LAs in 2023. Products were most commonly applied in a domestic setting, accounting for 72% of use.

Seasonal use of rodenticides

The season of rodenticide use was specified by all LAs returning rodenticide data. However, in at least one case, there were some sites for which the data were omitted. Overall, 99% of baiting was reported to occur "all year round", with very little rodenticide use being allocated to a particular season. This baiting pattern represents multiple baiting operations as well as permanent baiting. This differs from recent agricultural surveys, where approximately 60% of use occurs in autumn and winter, coinciding with the storage of harvested crops^{(2, 3)}. While this difference may be due to the different types of sites that dominate in LA rodenticide rodent operations, it is also possible that some LAs may have simply reported based on their policy of use rather than their actual use for 2023, or that data for application by season could not be easily extracted. Therefore, this seasonal distribution should be interpreted with caution.

Rodenticide bait type

Wax blocks were the most commonly used bait type in this survey, accounting for 49% by weight of all bait used (Figure 7). Grain baits were used in similar volumes, accounting for 43% by weight. Scatter packs, gel, pasta bait, grain-based pellets, pastes, soft wax and foam collectively made up the remaining 8% of bait types by weight. Of these, scatter packs accounted for 3.2% and pasta, soft wax and pellets for just over 1% each. The combined use of foam, paste and gel was less than 1%, by weight, of bait used.

The overall composition of the bait types encountered in this survey is similar to that reported in the 2015 LA survey⁽¹⁾, with both wax block and grain dominating. However, in 2015, wax block use was much greater than grain baits, with a respective 64% to 35% split compared to the much more even split in this survey. These LA survey findings are markedly different from those reported in previous agricultural surveys where grain baits dominate and wax baits are far less frequently encountered, making up only around five to 10% of total use^{(2, 3)}.

The type of bait selected is influenced by the setting of use. The high proportion of wax blocks being used is likely to be linked to the high proportion of baiting that LAs undertake in domestic settings, where it may be advantageous to use wax blocks which are manufactured with a central hole to allow them to be secured within bait boxes The use of wax blocks in bait stations reduces the likelihood of spillage and bait transference by rodents. This may be particularly important in domestic settings where exposure to domestic animals and householders, including children, must be prevented.

Figure 7 Type of rodenticide bait used by LAs in 2023

A column chart showing the percentage by weight of each bait type used by LAs in Scotland. Wax blocks and grain are the most commonly used bait types, accounting for 49% and 43% of baits respectively.

Target of rodenticide baiting

Survey respondents were asked to identify the target of their rodenticide use (Figure 8). Where these data were supplied, the most common target was recorded as a combination of rats and mice (59%), followed by rats (29%) and then mice (9%), with 3% of cases having no target stated. This contrasts with the 2015 survey⁽¹⁾ when rats alone dominated (59%) followed by a combination of rats and mice (35%) and 6% of use was targeted at mice alone. While the apparent substantial increase in baiting targeting both rats and mice might be reflective of an increase in combined infestations, it may also suggest that some LAs were unable to accurately summarise usage patterns and simply listed all use as 'rats and mice'.

Figure 8 Target of rodenticide use by LAs in 2023

A column chart showing the percentage by weight of rodenticide used for each target species by LAs in 2023. Rats and mice combined were the most common target, accounting for 59% of use.

Numbers of locations and visits

LAs were asked to provide data on the number of premises/locations at which rodent control took place and the number of visits undertaken. They were asked to separate their responses, if possible, by four categories of setting (Agricultural, Domestic, Industrial and Sewer), the 'Industrial' category included all other non-domestic, settings not covered by other categories.

Twenty seven LAs provided data on the number of locations/premises treated and the number of associated visits. Three of the responding LAs undertook rodent control on agricultural premises and only one of those in substantial numbers (>10 farms). The total number of agricultural premises covered was 66. The data is not considered further here as agricultural use of rodenticides is covered in other surveys^{(2, 3)}. No LAs reported undertaking any sewer baiting.

All 27 responding LAs undertook rodent control on domestic properties, but 10 of these provided no industrial data. Some local authorities stated that they were unable to separate out their domestic and industrial sites and some others indicated that they may have included some non-domestic properties in the domestic category. For the purposes of calculating the numbers of sites treated and the number of domestic and industrial visits have been combined.

There was a total of 26,591 domestic and industrial locations where rodent control took place. The total number of reported visits associated with these locations was 89,937. Some LAs acknowledged that their total visit data were estimated, and it is likely that additional LAs may have estimated visits but not stated this. Three LAs provided an estimated rate of visits per location that was then used to calculate a total figure.

A single LA provided raw location and visit data but around one third of locations had missing visit data. The average of visits per location for those locations with complete data was used to estimate the number of visits for locations with missing data.

Three LAs, reporting control at 4,769 locations, provided no visit data. Excluding these LAs, the average number of rodent control visits undertaken per location across the remaining LAs was 4.12 visits.